On the Influence of the Specific Gravities of Dispersed Materials on Their Agglomerability
Abstract Generated abstract
This study examines how the specific gravity of dispersed mineral materials affects their agglomerability during pelletizing, alongside moisture capacity, porosity, and compaction behavior. Samples of iron ore concentrate, ilmenite concentrate, quartz sand, limestone, and brown iron ore were prepared with granulometric compositions based on the Fuller equation, saturated by capillarity, and subjected to standardized vibrational compaction. The results show that higher specific gravity can favor faster compaction, but specific gravity alone does not explain agglomerability, as illustrated by differences between iron ore and ilmenite concentrates. The authors propose a coefficient incorporating maximum molecular moisture capacity, specific gravity, and minimum porosity after compaction as a more suitable indicator for evaluating the influence of material density on agglomeration behavior.
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On the Influence of the Specific Gravities of Dispersed Materials on Their Agglomerability
V. M. Vityugin, V. A. Trofimov
(Presented by the scientific seminar of the Department of OKhT)
Along with a favorable granulometric composition and optimal moisture content, an indispensable condition for the successful course of the pelletizing process is the presence, within the volume of the moist material, of special centers—embryos of pellets—and of certain compacting loads. The magnitude of the kinetic energy acquired during the rolling of pellets and which, ultimately, is expended on the displacement of grains and the compaction of the pellet, is determined not only by the rolling speed but also by the mass of the pellet. In this connection, the question of the influence of the specific gravities of dispersed materials on their agglomerability is of definite interest. To clarify the influence of this parameter on the pelletizing process, we prepared samples of materials with different specific gravities. The following were taken for the investigations: iron-ore concentrate, ilmenite concentrate, ground quartz sand, limestone, and brown iron ore. The granulometric composition of each material was selected in accordance with the Fuller equation
\[ y = 100 \sqrt{\frac{d}{D}}, \%, \]
where \(y\) is the content of each fraction, of size smaller than \(d\), %;
\(D\) is the maximum grain size, mm.
For all mixtures of materials, the indices of specific gravity, maximum molecular moisture capacity, capillary moisture capacity, and porosity of the materials under capillary saturation of a layer 100 mm high were determined. Modeling of the pelletizing process was carried out by vibrational compaction of a layer of moistened materials about 30 mm high. For this purpose, after capillary saturation, the weighed portion of material was transferred into the cup of an electromagnetic-type vibrator, in which 30 layers of filter paper were placed below and above the material layer. A light floating piston (surcharge) was placed on top to ensure better contact of the paper with the material, as well as for convenient reading of the height. Vibrational compaction was performed at a frequency of 100 Hz and an amplitude of 0.6 mm for 2 min. Simultaneously, the time at which the compaction process ended was recorded. After vibration treatment, the porosity and moisture content of the compacted specimens were determined. For an additional assessment of the compaction process, the volumetric index MMV was used, recalculated by the formula
Table 2
Comparative data on the agglomeration rate of various materials as a function of their specific gravities and other indicators
| No. | Materials | \(\gamma,\ \mathrm{g/cm^3}\) | MMV, % | KB, % | Porosity at capillary saturation, % | Compaction time, s | Layer porosity after compaction, % | At \(P_{\min}\), kg/mm, frac. units | \(W\) of briquettes, % |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Iron-ore conc. | 4,9 | 5,7 | 17,8 | 50 | 66 | 30 | 0,65 | 8,53 |
| 2 | Ilmenite conc. | 3,4 | 3,6 | 22,4 | 44 | 12 | 30 | 0,29 | 12,3 |
| 3 | Quartz sand | 2,54 | 9,9 | 29,4 | 54 | 88 | 26 | 0,72 | 14,27 |
| 4 | SSGOK limestone | 2,53 | 9,8 | 29,6 | 53 | 80 | 26 | 0,71 | 14,31 |
| 5 | Brown iron ore | 3,03 | 23,0 | 54,6 | 63 | 112 | 60 | 0,46 | 44,2 |
\[ K_{\mathrm{MMB}}=\frac{\mathrm{MMB}\cdot \gamma(100-\Pi)}{\Pi\cdot \gamma^{b}},\ \%, \]
where
\(K_{\mathrm{MMB}}\) — the amount of the total pore volume filled by MMB, %;
\(\mathrm{MMB}\) — the weight value of the maximum molecular moisture capacity, %;
\(\gamma\) — the specific gravity of the material, \(g/cm^3\);
\(\Pi\) — the porosity of the material layer, %;
\(\gamma^{b}\) — the specific gravity of water, taken in the calculations as equal to \(1\ g/cm^3\).
The results obtained are presented in the table.
As can be seen from the table, the rate of compaction to maximum density differs for different materials. Thus, for a material with a high specific gravity (for example, iron-ore concentrate, ilmenite concentrate), the rate of compaction is considerably higher than for materials with lower specific gravity. However, comparing iron-ore concentrate with ilmenite concentrate, we see that there is no such correlation. Indeed, the compaction rate of ilmenite concentrate is 5 times higher than the compaction rate of iron-ore concentrate, whose specific gravity is higher. The compaction process is more fully characterized by the expression for the relative content of MMB in the pore volume (\(K_{\mathrm{MMB}}\)), where the influence of the material’s specific gravity is expressed in relation to the indicator of maximum molecular moisture capacity. This equation for a layer of compacted material (\(K_{\mathrm{MMB}}\)) at \((\Pi min)\) may be recommended for evaluating the influence of the specific gravities of materials on their agglomerability, i.e.,
\[ A=\frac{\mathrm{MMB}\cdot \gamma}{\Pi min}(1-\Pi min); \]
where
\(A\) — a coefficient accounting for the influence of the specific gravities of materials on their agglomerability;
\(\mathrm{MMB}\) — the weight value of the maximum molecular moisture capacity of the material, in fractions of unity;
\(\gamma\) — the specific gravity of the material, \(g/cm^3\);
\(\Pi min\) — the minimum porosity of the layer of material obtained, for example, by vibrocompaction, in fractions of unity.